There are many different ways of detecting a subset of molecules in a fluid. Variations are from membranes, to chemical methods and biological processes. Many known processes utilize external forces for the filtration part, which can have detrimental effect on the filtrate. Other methods utilize a multi-step process with the initial step of filtering, followed by a detection step. This can lead to complex processes.
A one-step means for filtering and detecting a subset of molecules is relevant in a diverse field of technologies, ranging from food industry, to waste water treatment, drugs and medical devices.
Within the field of medical devices most traditional methods of filtering and detecting comprise large volumes of the fluid needing filtration. Detecting drugs in e.g. whole blood is often not possible and a larger volume whole blood is drawn from the patient due to the need of plasma for the analysis of the drug of interest. If the analysis is needed often the veins of the patient is punctured regularly and there is a risk of anemia for the patient.
Within the field of food industry, such as a dairy industry most traditional methods of filtering and detecting comprise filter paper, sieves and the like for visual inspection, spectrometry or bacterial counting of the residues. Disadvantages of this is large volumes are needed and that it is time consuming.
Within the field of environmental technologies, such as waste water analysis and treatment most traditional methods of filtering and detecting comprise filter papers, sieves and the like for spectrometry and bacterial counting of the residues. Disadvantages of this are the same as for the food industry; large volumes and time consuming.
One use of a porous mirror is in relation to detection of an analyte in a patient sample. The analyte can be any of a laboratory's test parameters for blood analysis which is detectable by light, e.g. spectrophotometry. Other approaches for measuring components present in a fraction of a fluid containing particles or other debris involve the separation of a fraction from cellular components by microfiltration techniques in e.g. a microfluidic device, prior to analysis of the fraction in a dedicated measurement in the microfluidic device. For example, a scientific article by Archibong et al. and published in Sensing and Bio-Sensing Research 3 (2015), p. 1-6, discloses a miniature measuring chamber for optically analyzing a plasma fraction that has been separated from a whole blood sample. In this type of device, a miniature microfluidic chamber is attached to the interface of an optical fiber. The bottom of the microfluidic chamber consists of a porous membrane that allows fluids and chemical compounds to flow inside the device, while at the same time filtering out undesired particles. The inside of the microfluidic chamber receiving the filtrate can be optically probed through a single optical fiber in normal-incidence reflection geometry.
However, such filtration-based approaches have several disadvantages when used for analyzing e.g. whole blood samples. Filtration devices inherently rely on a fluid flow of at least the filtrate through the pores of the filter from a sample feed to a filtrate analysis/measurement chamber. In through-flow geometries, the retentate (here the red blood cells) gradually clogs the filtration pores. In crossflow geometries, the retentate is lead along the surface of the filtering membrane, thereby reducing but not removing the problem with clogging, especially if the system is intended for repetitive use (more than 10-100 samples). Crossflow geometry also induces friction and shear interaction between the retentate and the surface of the filtering device. The disclosed device is most useful as a disposable rather than for continued and repetitive use, since a complete washout of a sample after measurement may be difficult or at least very time-consuming and unreliable, at the further risk of cross-contamination between subsequent samples. In this particular type of device, additional challenges for obtaining quantitative results from the optical probing may arise, due to pressure-induced deformation of the filtration membrane resulting in a change of the optical path for probing the filtrate.
Therefore, there is a need for an improved device and method for the detection of an analyte in a fluid with a fast and reliable response. More generally, there is a need for an improved device and method for the detection of substances in a fraction of a whole blood sample with a fast and reliable response.
Object of the present invention is to provide an improved detection overcoming at least some of the disadvantages of known sensors, systems and or methods for detecting substances in the plasma fraction of a whole blood sample, and in particular for detecting an analyte in a fluid.
The advantage of the present invention is that the filtration is performed by diffusion where no external energy is needed and the diffusion is also fast so that measurement on the liquid that have diffused into the pores of the porous mirror can be performed shortly after the fluid has been introduced into the porous mirror. The porous mirror is simple, with few parts and none that needs moving or changing position during filtration and measurement. The porous mirror is small in size and the volume needed for a measurement is very small compared to regular filtration devices. The porous mirror could be included into other applications or devices where filtration and subsequent measurement is needed on a fluid.